Conventionally, have been studied a method of collecting and removing acid gases, in particular, CO2 that are contained in gases (treatment object gases), for example various industrial gases manufactured in chemical plants such as a natural gas and a synthesis gas and flue gases, and various methods have been proposed.
For example, for the flue gases, have been actively studied a method of bringing CO2 in a flue gas into contact with an alkanolamine solution or the like to remove and collect CO2, and a method of storing CO2 without emitting CO2 to the atmosphere.
As the alkanolamine, it is possible to use monoethanolamine (MEA), 2-methylaminoethanol, 2-ethylaminoethanol, 2-propylaminoethanol, n-buthylaminoethanol, 2-(isopropylamino)ethanol, and 3-ethylaminoethanol.
For example, an absorbing-solution formed of a mixture of secondary amine or a mixture of secondary amine and tertiary amine is disclosed in a United States Patent specification. It is proposed that this mixed absorbing-solution is an advantageous absorbing-solution because an absorbing ability and regeneration energy are substantially improved in the mixed absorbing solution compared with an MEA single absorbing solution (Patent Document 1).
When a monoethanolamine (MEA) absorbing solution is used, there is a problem in that degradation in the absorbing-solution severely progresses because of oxygen or the like in gas.
Therefore, conventionally, a method has been proposed for stabilizing an absorbing-solution by adding, for example, trialkanolamine or methyldiethanolamine (MDEA) to the absorbing-solution (Patent Document 2 and Patent Document 3).
Patent Document 1: U.S. Pat. No. 5,618,506 specification
Patent Document 2: U.S. Pat. No. 3,535,260 specification
Patent Document 3: U.S. Pat. No. 4,840,777 specification